2010 BGD Practical 12 - Third Trimester

From Embryology
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Practical 12: Embryo to Fetus | Second Trimester | Third Trimester | Birth | Neonatal | Abnormalities


Introduction

Historic drawing of the fetus in the uterus at 8 months compared to non-pregnant uterus size.
  • Fetal Neural
  • Fetal Respiratory
  • Fetal Cardiovascular
  • survival issues for early delivery
  • fetal weight
  • fetal origins hypothesis

Practical Audio

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BGD Cycle A 2010 Audio - Dr Mark Hill Monday 17th May 2010 3-5pm G2G4.

Note - this is a live unedited recording from the practical and may contain errors in either descriptions or content.

listen Part 5 | download (820 Kb MP3 6:59)

Week 24+

  • Earliest potential survival expected if born
  • Respiratory Week 24 to 40 lung histology - terminal sac, end month 6 alveolar cells type 2 appear and begin to secrete surfactant
    • saccule - a large thin-walled airspace lined by flattened epithelium present from about 28 weeks gestation to 2 months after birth
  • Gonad - male gonad (testes) descending (week 30) Development Animation - Testis Descent
    • 10 to 23 weeks - (9.45%) had migrated from the abdomen and were situated in the inguinal canal
    • 24 to 26 weeks - (57.9%) had migrated from the abdomen
    • 27 to 29 weeks - (16.7%) had not descended to the scrotum
Testis 001 icon.jpg Testis Descent Failure of descent (cryptorchidism) either unilateral or bilateral testicular descent, occurring in up to 30% premature and 3-4% term males.


References: Sampaio FJ, Favorito LA. Analysis of testicular migration during the fetal period in humans. J Urol. 1998 Feb;159(2):540-2. | Malas MA, Sulak O, Ozturk A. The growth of the testes during the fetal period. BJU Int. 1999 Oct;84(6):689-92.

Fetal Weight

Fetal weight change.jpg

Fetal Birth

Most of the serious illness and mortality is concentrated in the 1 to 2 percent of infants who are born at less than 32 weeks of gestation (week 30) and who weigh less than 1500 g.


Teratogens - Infant Drug Clearance

Drug clearance rates

Teratogen (Greek, teraton = monster) Any agent that causes a structural abnormality following exposure during pregnancy. The overall effect depends on dosage and time of exposure.

The drug clearance data below are only approximate calculated rates for the fetus and infant from NZ Drug Safety in Lactation

Post-conceptual Age (weeks) Clearance of Drug (percentage of adults)
24-28 5%
28-34 10%
34-40 33%
40-44 50%
44-68 66%
> 68 100%


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Practical 12: Embryo to Fetus | Second Trimester | Third Trimester | Birth | Neonatal | Abnormalities


Additional Information

The following information is a detailed timeline of third trimester development and content does not form part of the current practical class.

Third Trimester

(Clinical Week 28)


Week
Stage
Event
Clinical third trimester Fetal size change.jpg Sense - Hearing 3rd Trimester - vibration acoustically of maternal abdominal wall induces startle respone in fetus.
27
 
28
  Respire Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and sacs
29
 
30
   

Genital male gonad (testes) descending

31
 
32
   
33
  Neural brain cortical sulcation - primary sulci present PMID:11158907
34
  Neural brain cortical sulcation - insular, cingular, and occipital secondary sulci present PMID:11158907
35
   
36
  Frazer006 bw600.jpg
37
   
38
Birth Newborn.jpg Clinical Week 40

Heart pressure difference closes foramen ovale leaving a fossa ovalis

Thyroid TSH levels increase, thyroxine (T3) and T4 levels increase to 24 h, then 5-7 days postnatal decline to normal levels

Adrenal - zona glomerulosa, zona fasiculata present




Glossary Links

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2010 BGD: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12

Cite this page: Hill, M.A. (2019, September 16) Embryology 2010 BGD Practical 12 - Third Trimester. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_BGD_Practical_12_-_Third_Trimester

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G